This research program has to do with photoreceptor cells, and it has two distinct foci: I -- The photoreceptor cells of arthropods exhibit even higher rates of membrane renewal than do vertebrates. Their visual pigments, on the of membrane renewal than do vertebrates. Their visual pigments, on the other hand, do not ordinarily bleach in the light. Regeneration of arthropod visual pigment frequently involves de novo synthesis of opsin rather than chromophore exchange, but the means by which 11-cis retinoid is restored are not clear. In some species there is evidence for a violet-sensitive photoisomerase, and a soluble protein with appropriate properties have been found in honeybees. Moreover, some arthropods employ 3- hydroxyretinal in their visual system. Understanding of alternate molecular strategies is a prerequisite for deeper understanding of the vertebrate visual system. The fate of the several geometric isomers of retinal, retinol, retinyl esters, and their 3-hydroxy analogues will be studied by high performance liquid chromatography (HPLC) in selected key species as a function of the daily rhythm of membrane shedding and of light and dark adaptation. The several retinoid binding proteins will be purified and their spectral, catalytic and other properties explored. Antibodies will be made to some of these proteins, so that they can be localized in the tissue by light and electronmicroscopy. The cellular distribution of the 3-dehydro- retinal-based visual pigment of the crayfish will be measured by microspectrophotometry (MSP). II -- The peripheral basis of avian color vision will be further examined. Spectral sensitivity functions of individual cones will be measured by using suction pipettes to record their photocurrents. This work will be correlated with additional measurements of the carotenoid composition, absorbance, and fluorescence of cone oil droplets, using MSP as well as spectrofluorometry and spectrophotometry of the pigments following extraction and separation by HPLC.